Speculatively fix build bots

This should address the issue found in:
https://lab.llvm.org/buildbot/#/builders/215/builds/4610

Author: AaronBallman

bolt/test/X86/Inputs/asm_main.c

@@ -1,3 +1,5 @@
+void foo(void);
+
 int main() {
   foo();
   return 0;